It is known from the prior art that polyurethane elastomers having short demould time and improved green strength can be prepared using low unsaturation polyoxypropylene polyols having from 1 to about 20 weight percent internal oxyethylene moieties. The elastomers thus prepared exhibit a low water absorption. A further improvement in green strength and demould is possible through the use of polyol blends having multimodal molecular weight distribution coupled with low unsaturation. These same polyols may be used to prepare haze-free polyoxyethylene capped polyols containing 1-20% by weight of random internal and 5-25% by weight of capped oxyethylene groups. The use of low unsaturation polyoxypropylene/polyoxyethylene polyols containing up to about 30 weight percent oxyethylene moieties based on the weight of said polyoxypropylene/polyoxyethylene polyol, at least a portion of which are random, internal oxyethylene moieties, in isocyanate-terminated prepolymers for the preparation of polyurethane elastomers having short demould time and improved green strength is also known in the prior art. Further, the preparation of elastomers from polyols having a high oxyethylene content, from polyisocyanates comprising at least 85% by weight of 4,4′-MDI or a variant thereof and from water has been disclosed in the prior art. The prior art also discloses a RIM process using a prepolymer from uretonimine-modified MDI and a polyether triol having a molecular weight of 400-6000 and an oxyethylene content of 10-85% by weight and using a polyether polyol having 65-100% by weight of oxyethylene units and an aromatic diamine. Short demould times are reported.
Co-pending application WO 00/55232 discloses a process for making a moulded polyurethane material, like an elastomer, by reacting 4,4′-diphenylmethane diisocyanate or a variant thereof, a polyol having a high oxyethylene content and water. Repetitive mouldings can be made without the need to treat the mould for easy demoulding after the first part has been made.